Picritic basalts from the Siqueiros transform fault

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doi: 10.2973/dsdp.proc.54.106.1980
Author(s): Schrader, Edward L.; Rosendahl, Bruce R.; Furbish, William J.; Meadows, George
Author Affiliation(s): Primary:
Duke Univ., Dep. Geol., Durham, NC, United States
Other:
Emory Univ., United States
Volume Title: Leg 54 of the cruises of the drilling vessel Glomar Challenger; Cristobal, Panama Canal Zone to Long Beach, California; May-June 1977
Volume Author(s): Powell, Robert, editor; Rosendahl, Bruce R.; Hekinian, Roger; Briqueu, Louis; Dmitriev, Yuri; Fodor, Ronald V.; Goll, Robert M.; Hoffert, Michel; Humphris, Susan E.; Mattey, David P.; Natland, James H.; Petersen, Nikolai; Roggenthen, William; Schrader, Edward L.; Srivastava, Ramesh K.; Warren, Nick; Barron, John A.; Bukry, David; Lynts, George W.
Source: Leg 54 of the cruises of the drilling vessel Glomar Challenger; Cristobal, Panama Canal Zone to Long Beach, California; May-June 1977, Robert Powell, Bruce R. Rosendahl, Roger Hekinian, Louis Briqueu, Yuri Dmitriev, Ronald V. Fodor, Robert M. Goll, Michel Hoffert, Susan E. Humphris, David P. Mattey, James H. Natland, Nikolai Petersen, William Roggenthen, Edward L. Schrader, Ramesh K. Srivastava, Nick Warren, John A. Barron, David Bukry and George W. Lynts. Initial Reports of the Deep Sea Drilling Project, Vol.54, p.71-80. Publisher: Texas A & M University, Ocean Drilling Program, College Station, TX, United States. ISSN: 0080-8334 CODEN: IDSDA6
Note: In English; illus.
Summary: Fresh, glassy picritic basalts have been recovered in a dredge haul in the Siqueiros transform fault near its intersection with the crest of the East Pacific Rise (EPR). Whole-rock and probe analyses of fresh glass from pillow margins demonstrate that these are the most primitive basalts so far found in the E Pacific. MgO in the glass is 11.3%. Variations in the compositions of the picrites result from accumulation of olivine (Fo89-86) and spinel phenocrysts. Olivine spherulites are abundant near the glassy rims. Orthopyroxene (bronzite) and plagioclase crystallites and spherulites also grew near pillow margins. The phenocrysts enclose trapped glasses which are even more primitive than the glass selvages. Fractionation of olivine and spinel would produce the other less primitive olivine-bearing tholeiites found in the area, which in turn would give rise to the abundant ferrobasalts of the area by crystal fractionation. It is thus proposed that olivine- rich basalts with magnesian glasses such as the picrites are the probable parents of the entire E Pacific mid-ocean ridge tholeiite suite. The widespread occurrence of ferrobasalts and other fractionated basalts erupted from the axial summit of the EPR implies that they were tapped from shallow levels in the axial magma reservoir, whereas the picrites were tapped from deeper levels along cross-cutting fracture-zone faults.
Year of Publication: 1980
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 05 Petrology, Igneous and Metamorphic; Basalts; Composition; Deep Sea Drilling Project; East Pacific; East Pacific Rise; Faults; Fracture zones; Genesis; IPOD; Igneous rocks; Leg 54; Magmas; North Pacific; Northeast Pacific; Pacific Ocean; Petrology; Picrite; Siqueiros fracture zone; Strike-slip faults; Transform faults; Ultramafic composition; Volcanic rocks
Coordinates: N082230 N082230 W1034036 W1034036
Record ID: 1981038719
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom